Hey guys! I am doing an experiment to determine my unknown. The problem is i had
ID: 81373 • Letter: H
Question
Hey guys!
I am doing an experiment to determine my unknown. The problem is i had contamination!
The first time i did gram stain, i had purple rods. I streaked the colonies on lb ajar, it usually just looks round and creamy yellowish colonies. On blood agar, it ate up some parts the ajar where you could see through the plate. They were off white colonies. It grew on mannitol salt agar with white streaks, not yellow. I also got dark black streaks on EMB.
On the next streak i did the next week, I got had different results! :( I got pink cocc. I got dark (brownish?) streaks (some even looked dark blue), but it did not grow at all on mannitol.
On my next gram stain, purple cocci! :(
I also did catalase test and it was positive, and an oxidase test and it was negative.
Here are the possibilities: Bacillus subtilis, E. coli, Pseudomonas aeriginosa, Salmonella enterica, serratia marcescens, s. aureus, s. pyogenes, p. vulgaris and m. luteus.
I am very confused. Please help because I have no chance to do any more tests. I have to use what I have. I thankfully appreciate it.
Explanation / Answer
according to your first interpretation, it is gram-positive ROD shaped, capable of producing hemolysin which degrades blood (common beta-hemolysin streptococcus family)
on next streak you got pink cocci/brownish colonies. but have not mentioned on which plate. LB agar or blood agar. if i assume blood agar then, it is cocci and beta-hemolysin producing organism unable to consume Mannitol. also in Gram stain, you got purple cocci. since you got cocci we remove rod shaped organism E. coli, Pseudomonas aeruginosa, p. vulgaris and Bacillus subtilis
now catalase test and oxidase test-
catalase test positive- s. aureus, serratia marcescens, m. luteus
out of these 3, serratia marcescens is Gram negative.
from rest of two m. luteus is oxidase positive
so you might got contamination of s. aureus.